We know that when problems relating to the engines of an aircraft lead to complete engine failure, in addition to having zero thrust, the aircraft may lose its electrical power supply necessary for operation of its systems. In order to remedy the lack of power usually provided by the engines, the aircraft is generally provided with a dynamic air turbine of the RAT type (“Ram Air Turbine”), making it possible to supply a certain amount of power to the control systems of the aircraft. It includes propellers deployed on the exterior of the fuselage, which are set in rotation under the effect of the displacement of the aircraft and drive the said turbine. The detection of a complete failure of the engines, combined with the activation of the ram air turbine, is called a TEFO event (“Total Engine Flame Out”).
However, during a TEFO event the engine thrust may be insufficient for the autopilot and the flight director to be able to correctly guide the aircraft in certain modes, in particular in level flight or when climbing.
For example, the performance of the automatic pilot system depends upon the guidance mode in which the aircraft is situated. Thus, in a guidance mode configured to make the aircraft descend with a reduced engine thrust and a fixed speed, of the OP DES type (“Open Descent”), the automatic pilot system functions correctly.
On the other hand, for guidance modes configured to maintain the altitude of the aircraft, of the ALT (altitude) type, or also to reach a higher altitude, of the ALT* type, since these two modes require a significant engine thrust the automatic pilot system may not have sufficient power to ensure the guidance. It may then be difficult for the automatic pilot system to guide the aircraft.
In the first case it is considered that the guidance mode and the automatic pilot system are compatible, whilst in the second case they may be considered incompatible.
The problem and the consequences are similar with respect to the flight director. For example, when an altitude hold is required in ALT mode, the automatic pilot system and the flight director cannot ensure the monitoring of this altitude entered via a flight control unit of the FCU type (“Flight Control Unit”), since the aircraft may not have sufficient engine thrust.
Thus, during an event of the TEFO type there are two different situations, each requiring specific actions by the pilots. In a first case corresponding to a guidance mode different from the OP DES mode, the pilots must manually disconnect the flight director if they use it in manual flight mode; and if they are in automatic pilot mode the automatic pilot system must also be disconnected manually.
On the other hand, in a second case corresponding to a guidance mode of the OP DES type, the pilots can continue to monitor the indications of the flight director in manual flight mode, or can also let the automatic pilot system continue the guidance of the aircraft if this latter is engaged.
Furthermore, when the aircraft undergoes a TEFO event, the autothrottle which controls the engine thrust can no longer ensure the management, since the engines have failed. Consequently, the autothrottle should be deactivated by the pilots in order to continue the flight, regardless of the guidance mode used, even with the OP DES mode.
Other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.